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Most themes, when displaying the comment form, change the HTML to pre-fill username, email address, and website when comment cookies are received in the HTTP request. Since the response does not have explicit nocache headers, per RFC2616 (http://www.ietf.org/rfc/rfc2616.txt) intermediate caches can use heuristics to determine the cache TTL for the response. Since there is 0 freshness data in the response, it is not really possible to perform good heuristics, but in practice, caches will assign a default TTL to this type of response. The result is that private information input by user A when submitting a comment can be returned to user B when making a request for the same URL.

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To protect ourselves against this, we should call nocache_headers() when comment cookies are sent and the comment form is being displayed. Alternatively, we can send nocache headers for all requests with comment cookies regardless of the content form being displayed or not (probably easier and maybe safer).

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To protect ourselves against this, we should call nocache_headers() when comment cookies are sent and the comment form is being displayed. Alternatively, we can send nocache headers for all requests with comment cookies regardless of the comment form being displayed or not (probably easier and maybe safer).

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http://humboldtherald.wordpress.com/2011/01/27/gremlins/ is a story likely caused by an aggressive cache and the lack of nocache headers.